The invention relates to a method for producing a cigarette filter unit in which a sequence of filter elements are disposed on a continuously supplied porous or perforated covering strip, are at least partially wrapped thereby and are adhesively joined and the filter strand formed in this manner is subdivided by a cutting device, apparatus for performing the method and a cigarette filter unit produced in accordance with the method.
In the production of cigarette filters which are provided with porous or perforated covering strips it is known for the side of the covering strip that is to be joined to the plug-like filter elements to be completely provided with an adhesive substance. This procedure suffers from disadvantages in that after adhesive joining of the covering strip to the filter elements on the one hand at least a substantial proportion of the porous or perforated places is adhesively joined, and air permeability is substantially reduced, and on the other hand the degree of air permeability of a covering strip coated in this manner fluctuates from filter to filter over an excessive range, so that a precise statement of the percentage of smoke constituents still contained in the cigarette smoke after flowing through such a cigarette filter cannot be stated.
When using porous or perforated covering paper it would be feasible, in order to avoid the above-mentioned disadvantages, to apply the adhesive substance in thin strips along the longitudinal orientation of the covering paper strip and/or perpendicularly to the longitudinal orientation of the latter. All these solutions would however suffer from the disadvantage that subsequent adhesive joining in the same way of a cigarette filter produced in this manner by means of a porous or perforated connecting paper for connection to the tobacco part would result in substantial variation in mutual overlapping of the adhesive places, and therefore of the air permeability from filter to filter which, as already mentioned, is undesirable. If the covering paper strip were to be adhesively joined to the wrapped filter elements only by means of the adhesive strip, which extends in the longitudinal orientation of the filter, there would be a substantial risk that the slightest deformation of the filter cross-section would result in the formation of false air ducts extending along the longitudinal orientation of the filter, which in turn would result in a substantial change of the flavour and composition of the smoke inhaled by the smoker. Furthermore, such adhesive joining of the covering paper strip to the filter elements in a filter with a chamber containing free-flowing filter material would be unusable, because in tightly filled chambers there would be an excessive risk that a slight deformation of the filter cross-section would cause granulate particles to pass through the ducts formed between two adhesive strips into the mouth of the smoker, which would be extremely unpleasant for the latter. If the covering paper strip were to be adhesively joined to the filter elements only along the circumference of the filter elements which are to be wrapped along circles situated at a distance from each other, it would of course be impossible for the cutting places to be arranged so that they always extend through the relatively narrow adhesively joined ranges, so that the covering paper strip would be adhesively joined to the outside of the wrapped filter elements at the cutting places when the filter strand is cut into individual portions. However, if this is not the case, i.e. if the adhesive region is situated further towards the interior at a distance from the cutting place, the covering paper strip would project slightly from the wrapped filter element at the cutting place, and give rise to frequent defects in the filter machine by means of which the filters are joined to the tobacco part of the cigarette, as has been shown by tests.